Metal parts such as aluminum sheet panels are becoming increasingly popular in recent automotive body applications. For examples aluminum sheet panels are used for a closure panel assembly. The closure panel assembly typically includes an outer skin or panel with a generally perpendicular upstanding flange of about ten millimeters (10 mm) in height and an inner section or sheet panel completing the assembly. The closure panel assembly is pressed together in tooling known as a hemmer where the upstanding flange of the outer sheet panel is pressed down onto the inner sheet panel, thereby locking the panels together with a tightness prescribed by a product tolerance.
During vehicle body manufacturing, such aluminum sheet panels, particularly those about one millimeter (1 mm) in thickness, are formed into various shapes using a stamping process. However, through the shaping of the aluminum in the stamping process, the sheet panels are work hardened. The pressing down on the upstanding flange by the hemmer rotates the flange through about a ninety degree (90°) movement and the radius of this bend (5 mm) experiences stress cracks. Therefore, sections of the aluminum parts need to be annealed prior to the hemming process. Particularly, the radius of the upstanding flange around the perimeter of the outer sheet panel. The annealing of this area alleviates stress cracking in the final manufacturing.
Currently, an induction heating system is used to anneal the outer sheet panel. The induction system uses at least one electrical coil element that is formed to the outer perimeter of the outer sheet panel. An operator is used to load and unload the outer sheet panel into the induction system. An induction current is passed through the coil element to heat up the whole outer perimeter at once, which causes dimensional instability or distortion of the outer sheet panel. The distortion comes from the heat applied by the induction heating system all at once around the whole outer perimeter of the outer sheet panel. Further, because only three sides of the outer sheet panel are annealed to eliminate the distortion, the side not annealed is subject to stress cracking. In addition, if induction heating is used to do portions of the outer sheet panel at a time, separate induction cycles after cooling of the previous sections are not economical due to cycle time. Further, expensive tape is wrapped around the coil element to prevent the outer sheet panel from touching them, which needs to be changed on a daily basis, increasing maintenance costs and user intervention.
As a result, it is desirable to provide a method for laser annealing metal parts for automotive structures. It is also desirable to provide a method for laser annealing of aluminum sheet panels for a closure panel assembly, which prevents distortion of the assembly. It is further desirable to provide a method for laser annealing of aluminum hems in automotive closure components to enhance the bendability of the material during helming. Therefore, there is a need in the art to provide a method for laser annealing that meets these desires.